Deleting items while trying to add new ones

If there are a lot of elements on the screen, they start to get deleted when you try to add new ones.
The order in which you get the error is:

  1. insert a large number of items, so that a scroll bar appears
  2. drop to the bottom of the list and try to add an item.

I guess the reason is that the “Adding” button has a lower z-index than the “Remove” button on the item.

Closed to keep the conversation to the “Designer UX - the Screen-Data bar is not separated from the components” thread.